This invention relates to trunked radio frequency communications systems and methods, and more particularly to Single Channel Autonomous Trunking (SCAT) radio frequency communications systems and methods.
Trunked radio systems and methods are widely used by public safety organizations, transport companies, and other organizations for dispatch and other two-way communications within the organization. Trunked systems and methods may be used when high reliability and short access times are desired for short messages. In a trunked system, a plurality of duplex radio frequency communications channels and associated repeaters are shared among multiple mobile terminals. Each mobile terminal is able to transmit a communication such as a short message on any of the radio frequency channels. A mechanism is provided for temporarily allocating channels to calling and called mobiles on a demand basis. At the conclusion of the communication, the channel in use becomes de-assigned so that it is available for reassignment to other mobile terminals. Both analog and digital trunked radio communications systems and methods are presently employed. The design and operation of trunked radio frequency communications systems and methods are well known to those having skill in the art and need not be described further herein.
A particular trunked radio system and method, referred to as a Single Channel Autonomous Trunking (SCAT) communications system and method, provides control channel and working channel (also referred to as xe2x80x9cassigned channelxe2x80x9d) signaling over a single radio frequency channel. The single radio frequency channel operates alternately in a control channel mode and in a working channel mode, with the idle mode being the control channel mode. When the SCAT system is idle, control channel signaling is transmitted over the single channel. When a channel request is received, a channel assignment message is sent out in a standard manner via the control channel signaling and the single channel then begins operating as a working channel. At the conclusion of the working channel communication, the single channel reverts to the control channel mode in readiness for further channel assignments.
SCAT can thus offer an enhanced trunking solution that can provide trunked radio coverage in difficult coverage areas with low traffic. SCAT can permit public safety customers who are already part of a large network to extend their communications coverage over difficult areas, such as tunnels, large buildings and shopping centers, in a cost effective, frequency-efficient manner. SCAT can also be viewed as an enhanced single channel system that can provide all of the functionality of a conventional system, plus advanced digital trunking features, such as emergency, multi-group privacy and individual call capabilities. SCAT systems and methods are described in U.S. Pat. No. 5,408,680 to Hattey et al., entitled xe2x80x9cSingle Channel Autonomous Digitally Trunked RF Communications Systemxe2x80x9d, the disclosure of which is hereby incorporated herein by reference. A SCAT system that is marketed by the assignee of the present invention is described in a publication entitled xe2x80x9cConfiguration Manual, EDACS(copyright) Single Channel Autonomous Trunking (SCAT) GETC, LBI-38987Bxe2x80x9d, May 1994, pages 1-32, the disclosure of which is hereby incorporated herein by reference.
The present invention provides Single Channel Autonomous Trunking (SCAT) radio frequency systems and methods that use a single duplex Time Division Multiple Access (TDMA) channel for the control and working channels thereof. As is well known to those having skill in the art, in TDMA, a radio frequency channel is divided into sequential time slots. Communications occur using bursts of digital data transmitted during an assigned time slot. By providing a single duplex TDMA radio frequency channel including a plurality of TDMA time slots in SCAT systems and methods, the SCAT systems and methods can simultaneously operate in a control channel mode and a working channel mode using the single duplex TDMA radio frequency channel.
More specifically, SCAT systems and methods according to the invention include at least one SCAT repeater and at least one SCAT mobile terminal. Each SCAT repeater comprises a single duplex TDMA radio frequency channel including a plurality of TDMA time slots. At least a first one of the TDMA time slots is a SCAT control channel that receives working channel requests and that transmits working channel assignments. At least a second one of the TDMA time slots is a SCAT working channel that transmits and receives working channel communications in accordance with the working channel assignments.
SCAT mobile terminals according to the invention also comprise the single duplex TDMA radio frequency channel including the plurality of TDMA time slots. At least the first one of the TDMA time slots is the SCAT control channel that transmits working channel requests and that receives working channel assignments. At least the second one of the TDMA time slots is the SCAT working channel that transmits and receives working channel communications in accordance with the working channel assignments.
A SCAT repeater may also be regarded as including means for transceiving a single duplex TDMA radio frequency channel including a plurality of TDMA time slots. Means are also included for receiving SCAT working channel requests and for transmitting SCAT working channel assignments in at least a first one of the plurality of TDMA time slots. Means are also included for transmitting and receiving SCAT working channel communications in accordance with the working channel assignments in at least a second one of the plurality of TDMA time slots. SCAT repeater methods also may be provided.
A SCAT mobile terminal may also be regarded as including means for transceiving a single duplex TDMA radio frequency channel including a plurality of TDMA time slots. Means are also included for transmitting SCAT working channel requests and for receiving SCAT working channel assignments in at least the first one of the plurality of TDMA time slots. Means are also included for transmitting and receiving SCAT working channel communications in accordance with the working channel assignments in at least the second one of the TDMA time slots. SCAT mobile terminal methods also may be provided.
In one embodiment of the present invention, the TDMA radio frequency channel includes a frame having first and second TDMA time slots. One of the TDMA time slots is the SCAT control channel and the other of the TDMA time slots is the SCAT working channel. However, more than two TDMA time slots may be provided so that one or more TDMA time slots operates as a SCAT control channel and one or more TDMA time slots operate as a SCAT working channel.
Accordingly, SCAT repeaters and mobiles need not operate alternately in a control channel mode and in a working channel mode. Rather, SCAT repeaters and mobiles may simultaneously operate in a control channel mode and in a working channel mode using a single duplex radio frequency channel that is divided into a plurality of TDMA time slots. More efficient SCAT systems and methods may thereby be provided, that can allow more reliable communications and more rapid access to a working channel.
According to another embodiment of the invention, the at least a first one of the plurality of TDMA time slots is alternatingly a SCAT working channel that transmits and receives working channel communications in accordance with the working channel assignments. Thus, the at least a first one of the plurality of TDMA time slots may be alternatingly used as a SCAT control channel and a SCAT working channel, as was described in the Hattey et al. patent. SCAT repeaters and mobiles may simultaneously operate in a control channel mode and in a working channel mode and may also alternatingly operate in a control channel mode and a working channel mode. Thus, added channel capacity may be provided when desired.